Although osseointegrated dental implants generally have a high success rate, about 10% of implants fail. The broad objectives of this proposal are to identify microbial risk factors operative in implant failure, and assess the potential for antibacterial therapy in the prevention and treatment of failing dental implants. The first specific aim includes a predominant cultivable study of failing dental implants. The microbiotas of successful and failing osseointegrated implants will be compared. Implants will be Characterized by clinical measurements using standardized radiographs, attachment level, mobility, and inflammation including peri-implant temperature measurements. Microorganisms will be characterized using fluorescent substrate tests for biochemical reactivity, and polyacrylamide gel electrophoresis. Isolates will be identified by comparison of characteristics with those of reference strains of species, including new and reclassified species. Isolates of unknown species will be characterized by rRNA sequencing and DNA probes. The second specific aim will assess the potential of antibacterial treatment to treat failing Implants. Failing implants will be treated using a non-surgical, aggressive antimicrobial therapy. Implants will be monitored using the clinical measurements from the first specific aim. Successful treatment will be indicated by increases in bone density and/or height using subtraction radiography. The post-treatment microbiota of treated implants will be characterized using predominant cultural methods as in the first aim. Comparison of pre- and post-treatment microbiota from samples obtained from successfully and unsuccessfully treated implants will provide additional data to differentiate species associated with implant-failure. The long-term objective is to improve the success-rate of dental implants. Information from this proposal will contribute to determining specific treatment regimens for failing implants. The objective is to identify microorganisms that mediate, indicate or predict for implant success or failure. Preventive measures may then be devised to improve the probability of dental implant success.